Rubber-modified styrenci resin composition and molded article thereof

ABSTRACT

A rubber-modified styrenic resin composition comprising (A) 100 wt. parts of a rubber-modified styrenic resin which contains 10 to 35 wt. % of soft component particles having an average particle size of 0.1 to 0.5 μm, where said soft component particles have a single occlusion structure comprising a core part which consists of a single continuous phase of a styrenic resin and a shell part which comprises a rubber polymer and occludes said core part, and (B) 0.1 to 10 wt. parts of a polymer having a solubility parameter (SP) of 8.45 to 8.70 and having no aromatic vinyl compound unit therein. This composition has excellent plane impact strength and gloss properties as well as moldability and other physical properties, and satisfies properties required for exterior materials, wrapping materials and molded foam articles.

This application is a continuation-in-part of PCT internationalapplication No. PCT/JP95/01493 which has an international filing date ofSep. 26, 1995 which designated the United States, the entire contents ofwhich are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a rubber-modified styrenic resincomposition which provides a molded article which is excellent in planeimpact strength and gloss, and a molded article thereof. In particular,the present invention relates to a rubber-modified styrenic resincomposition which provides a molded article plane impact strength ofwhich is greatly increased, and gloss of which is excellent by theaddition of a specific polymer to a specific rubber-modified styrenicresin, and a molded article thereof.

DESCRIPTION OF CONVENTIONAL ART

In the fields of office automation equipments and household appliances,good balance of various properties such as processability in a moldingprocess, accuracy of finished sizes of processed products, mechanicalproperties (e.g. tensile strength, flexural strength, etc.), heatresistance, and so on is required. In particular, when a resin is usedas an exterior material, further improvement of gloss and plane impactresistance is required. In these years, such requirement reaches to avery high level. When the resin is used as a wrapping material, highlevel plane impact strength and appearance are required. When the resinis used as a cushioning material, one of the essential properties whichthe resin should have is good shock absorbability. However, therubber-modified styrenic resin does not necessarily satisfy all theabove requirements.

As a method for improving the impact resistance of the rubber-modifiedstyrenic resin, there is known the addition of specific amounts of anorganic polysiloxane and an ethylene-unsaturated carboxylate copolymerto the rubber-modified styrenic resin. However, the dispersed rubberparticles have an average particle size of 0.1 to 2.5 μm, and the planeimpact strength of the composition is insufficient.

SUMMARY OF THE INVENTION

An object of the present invention is to solve the above problems andprovide a rubber-modified styrenic resin composition excellent in theproperties which are required for the exterior materials, wrappingmaterials and molded foam articles, for example, excellent in planeimpact strength and gloss, as well as molding properties and otherphysical properties.

According to a first aspect of the present invention, there is provideda rubber-modified styrenic resin composition comprising (A) 100 wt.parts of a rubber-modified styrenic resin which contains 10 to 35 wt. %of soft component particles having an average particle size of 0.1 to0.5 μm, where said soft component particles have a single occlusionstructure comprising a core part which consists of a single continuousphase of a styrenic resin and a shell part which comprises a rubberpolymer and occludes said core part, and (B) 0.1 to 10 wt. parts of apolymer having a solubility parameter (SP) of 8.45 to 8.70 andcomprising no aromatic vinyl compound unit therein.

According to a second aspect of the present invention, there is providedan injection molded article, an extrusion molded article or a moldedfoam article comprising the above rubber-modified styrenic resincomposition.

DETAILED DESCRIPTION OF THE INVENTION

The rubber-modified styrenic resin (A) used in the present invention maybe a rubber-modified styrenic resin which is obtained by polymerizing atleast one styrenic monomer, or at least one styrenic monomer and acompound copolymerizable therewith in the presence of a rubber polymer.

Examples of the styrenic monomer which is used as a raw material of therubber-modified styrenic resin (A) used in the present invention arestyrene,α-alkyl-substituted styrenes such as α-methylstyrene, nucleussubstituted alkylstyrenes such as p-methylstyrene, and so on. Examplesof the compound copolymerizable with the styrenic monomer are vinylmonomers such as acrylonitrile, methacrylonitrile, methacrylic acid,methyl methacrylate, etc., maleic anhydride, maleimide, nucleussubstituted maleimide, and so on.

As the rubber polymer, polybutadiene, styrene-butadiene copolymers,ethylene-propylene-non-conjugated diene terpolymers, and so on are used.Among them, polybutadiene and the styrene-butadiene copolymers arepreferred. As the polybutadiene, high-cis polybutadiene having a highcis-structure content and low-cis polybutadiene having a lowcis-structure content are both used.

A content of the soft component particles in the rubber-modifiedstyrenic resin (A) is from 10 to 35 wt. %. When this particle content isless than 10 wt. %, the plane impact strength is not sufficientlyimproved, while it exceeds 35 wt. %, properties other than the planeimpact strength, for example, stiffness, heat resistance, etc. aredeteriorated unpreferably.

A content of the soft component particles in the rubber-modifiedstyrenic resin (A) is measured as follows:

About 0.5 g of a sample of the rubber-modified styrenic resin is weighed(weight: W₁), and the sample is dissolved in a mixed solvent of methylethyl ketone and methanol (a volume ratio of 10/1) (50 ml) at roomtemperature (about 23° C.). Then, undissolved components are isolated bycentrifugation, dried, and then weighed (weight: W₂). A content of thesoft component particles in the rubber-modified styrenic resin iscalculated by the equation:

    (W.sub.2 /W.sub.1)×100 (%).

An average particle size of the soft component particles are from 0.1 to0.5 μm, preferably from 0.1 to 0.3 μm. When the average particle size isless than 0.1 μm, the plane impact strength of the molded article is notsufficiently improved, while when it exceeds 0.5 μm, the appearance ofthe molded article such as gloss is deteriorated unpreferably.

Herein, the average particle size is defined as follows:

A very thin section of the rubber-modified styrenic resin is prepared,and its transmission electron microscopic photograph is taken. Particlesizes of the soft component particles in the photograph are measured andthe average particle size is calculated by the following equation:

    Average particle size=Σn.sub.i D.sub.i.sup.2 /Σn.sub.i D.sub.i

wherein D_(i) is a particle size, and n_(i) is the number of theparticles having the particle size D_(i).

In the present invention, the soft component particles in therubber-modified styrenic resin (A) should have a single occlusionstructure comprising a core part which consists of a single continuousphase of a styrenic resin and a shell part which comprises a rubberpolymer and occludes said core part, which structure may be referred toas a core-shell structure or a capsule structure. The gloss isdeteriorated when the particles have other structure, for example, asalami-like structure in which plural minute particles of the styrenicresin are dispersed in a continuous phase of the rubbery polymer. Thestructure of the soft component particles is observed with atransmission electron microscope as in the above measurement of theaverage particle size.

The synthesis of the rubber-modified styrenic resin (A) in which thestructure of the soft component particles is the single occlusionstructure is described in, for example, Die Angewandte MacromolekulareChemie, 58/59, 175-198 (1977), and such resin can be synthesized bypolymerizing a styrenic monomer in the presence of a styrene-butadieneblock copolymer having a styrene content of 15 to 65 wt. %.

According to the present invention, the composition contains 0.1 to 10wt. parts of a polymer (B) having a solubility parameter (SP) of 8.45 to8.70 and comprising no aromatic vinyl compound unit therein per 100 wt.parts of the rubber-modified styrenic resin (A). When the content of thepolymer (B) is less than 0.1 wt. part, the plane impact strength is notsufficiently improved, while when it exceeds 10 wt. parts, otherphysical properties such as heat resistance are deterioratedunpreferably.

The content of the polymer (B) in the composition of the presentinvention can be obtained by preparing a very thin section of thecomposition, taking a transmission electron microscopic photograph ofthe slice piece, calculating an a percentage of areas of the polymer (B)in the whole photographic area, and converting the percentage to thecontent of the polymer (B). Alternatively, a method using a spectrometersuch as a NMR spectrometer or an IR spectrometer and calculating thecontent of the polymer (B) from an absorption peak, or a methodcomprising fractionating the polymers with a solvent may be used.

The solubility parameter (SP) of the polymer (B) used in the presentinvention is from 8.45 to 8.70. When the solubility parameter is largerthan 8.45 or smaller than 8.70, the improvement of the plane impactstrength is insufficient.

Herein, the solubility parameter is defined as an attraction forcebetween molecules according to the Hildebrand-Scatchard theory. Thistheory is described in "The Solubility of Nonelectrolytes", ThirdEdition, Reinhold Publishing Corp., New York, 1949, and Chem. Rev., 8,321 (1931), as well as common textbooks in the polymer chemistry. Thesolubility parameter can be experimentally measured by a viscositymethod or a swelling method, or calculated from molecular structures,and values of the solubility parameter differ slightly depending on themethods. Herein, there is used a method for calculating the solubilityparameter from the molecular structures which is proposed by Small. Thismethod and theory are described in detail in J. Appl. Chem., 3, 71-80(1953), the disclosure of which is hereby incorporated by reference.According to this literature, the solubility parameter is calculated bythe following equation: ##EQU1## wherein F_(i) is a molar attractingforce of a structural group which constitutes a molecule such as anatom, an atomic group or a bond type, V is a molar volume, p is adensity, and M is a molecular weight of a compound, or a molecularweight of one repeating unit (namely a monomer) in the case of a polymermolecule. As the F_(i) values, those of Small described in the above twoliteratures are used. Each of ρ, ΣF_(i) and M of a copolymer iscalculated as a sum of a product of ρ, ΣF_(i) or M of a homopolymer ofeach monomer and a molar percentage of the respective monomer.

The polymer (B) used in the present invention is a polymer which has noaromatic vinyl compound unit therein. When the resin compositioncontains a polymer which comprises an aromatic vinyl compound unit, theplane impact strength is low.

Examples of the aromatic vinyl compound are styrene, α-alkyl-substitutedstyrenes such as α-methylstyrene, nucleus substituted alkylstyrenes suchas p-methylstyrene, and so on.

Examples of the polymer (B) having the solubility parameter of 8.45 to8.70 are copolymers comprising ethylene and at least one vinyl monomerselected from the group consisting of unsaturated carboxylic acids,unsaturated carboxylates and vinyl acetate. Specific examples of suchcopolymer are ethylene-unsaturated carboxylic acid copolymers,ethylene-unsaturated carboxylate copolymers, ethylene-vinyl acetatecopolymers, ethylene-unsaturated carboxylate-vinyl acetate terpolymers,copolymers comprising ethylene and at least two unsaturatedcarboxylates, and so on.

Examples of the unsaturated carboxylic acid are acrylic acid,methacrylic acid, etc. Examples of the unsaturated carboxylate are ethylacrylate, methyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate,glycidyl acrylate, methyl methacrylate, ethyl methacrylate, 2-ethylhexylmethacrylate, stearyl methacrylate, glycidyl methacrylate, etc.

Preferred examples of the copolymer comprising ethylene and at least onevinyl monomer selected from the group consisting of unsaturatedcarboxylic acids, unsaturated carboxylates and vinyl acetate which areused in the present invention are ethylene-acrylic acid copolymers,ethylene methacrylic acid copolymers, ethylene-methyl methacrylatecopolymers, ethylene-ethyl methacrylate copolymers, ethylene-ethylacrylate copolymers, ethylene-methyl acrylate copolymers, ethylene-vinylacetate copolymers, ethylene-methyl acrylate-glycidyl methacrylatecopolymers, ethylene-methyl methacrylate-glycidyl methacrylatecopolymers, ethylene-vinyl acetate-glycidyl methacrylate copolymers,etc.

Percentages of the above vinyl monomer and ethylene in the copolymer maybe arbitrarily selected in a range in which the copolymer having thesolubility parameter (SP) of 8.45 to 8.70 is obtained. A percentage ofthe above vinyl monomer in the copolymer is preferably from 5 to 60 wt.%. There is no limitation on a bonding type between the vinyl monomerand ethylene (e.g. random, block, alternating, etc.). A melt flow rateof the copolymer (measured according to JIS K7210 at 190° C. under aload of 2.16 kgf) is not limited, and preferably from 1 to 500 g/10 min.

When the composition of the present invention comprises 0.01 to 0.5 wt.part of an organic polysiloxane per 100 wt. parts of the rubber-modifiedstyrenic resin (A), the plane impact strength is further improved. Whenthe amount of the organic polysiloxane exceeds 0.5 wt. part, the planeimpact strength will not increase further.

Herein, the organic polysiloxane is intended to mean a compound of thefollowing formula: ##STR1## wherein R₁ and R₂ are the same or differentand represent an alkyl group, an aryl group or a phenyl group, and n isan average degree of polymerization and a number of 10 to 1500. Thepolysiloxane may have an epoxy group, an amino group, a carboxyl group,a vinyl group, a hydroxyl group, a fluorine atom or an alkoxy group atits terminal or intermediate molecular chain.

A structure of the organic polysiloxane to be used in the presentinvention may be a homopolymer, a random copolymer, a block copolymer ora graft polymer, or the polysiloxane may be one in which a part of theorganic groups are substituted by a hydroxyl group, an alkoxy group, ahydroxyalkyl group, etc. Further, two or more organic polysiloxanes maybe used in combination.

A kind of the organic polysiloxane to be used in the present inventionis not limited. Specific examples thereof are polydimethylsiloxane,polymethylphenylsiloxane, polydiphenylsiloxane, and so on. A viscosityof the organic polysiloxane is not critical. When the viscosity is lessthan 10 cSt, volatility is too large, while it is larger than 100,000cSt, it may be difficult to disperse the organic polysiloxane in thecomposition homogeneously.

In general, one having the viscosity in the range from 10 to 100,000 cStat 30° C. is preferred because of easy handling.

A method for the addition of the organic polysiloxane is not limited.For example, the organic polysiloxane can be added in the course of thepreparation of the rubber-modified styrenic resin (A), for example, theorganic polysiloxane can be beforehand added to the monomer in thepolymerization step or added to the polymerization system in the courseof polymerization. Alternatively, the organic polysiloxane may be addedwhen the components (A) and (B) are mixed, or when the composition ismolded. These methods may be employed independently or in combination.

To prepare the rubber-modified styrenic resin composition of the presentinvention, determined amounts of the components are dry blended using amixing apparatus such as a Henschel mixer, a tumbling mixer, and so on,or heated and kneaded at a temperature of 180 to 260° C. using akneading apparatus such as a single or twin screw extruder, a Banburymixer, and so on, and then the mixture is pelletized. If necessary,additives such as an antioxidant, a heat stabilizer, a UV-lightabsorber, a lubricant, an antistatic agent, a mineral oil, and so on maybe added to the composition.

The injection molded article comprising the rubber-modified styrenicresin composition of the present invention can be produced using aconventionally used injection molding apparatus.

The extrusion molded article comprising the rubber-modified styrenicresin composition of the present invention can be produced using aconventionally used extrusion molding apparatus.

There is no specific limitation on a method for the production of theextrusion molded article by extruding the rubber-modified styrenic resincomposition of the present invention. There are exemplified a methodcomprising melting the resin composition in an extruder and extruding itthrough a T-die, and a method comprising extruding the molten resincomposition in a sheet form from the extruder and then biaxiallystretching it by a tenter or an inflation method.

There is no specific limitation on a method for the production of a foamarticle by foaming the rubber-modified styrenic resin composition. Thereare exemplified a method comprising melt kneading the rubber-modifiedstyrenic resin composition and a decomposable foaming agent by anextruder and foaming the mixture, a method comprising melting therubber-modified styrenic resin composition by the extruder, adding avaporizable foaming agent directly to the composition under pressure ina middle part of a cylinder, kneading them and foaming the mixture, amethod comprising impregnating small pellets or beads of therubber-modified styrenic resin composition with a vaporizable foamingagent in the extruder or an aqueous suspension and foaming theimpregnated pellets or beads with steam.

Examples of the decomposable foaming agent are azodicarbonamide,trihydrazinotriazine, benzenesulfonylsemicarbazide, etc. Examples of thevaporizable foaming agent are propane, n-butane, isobutane, n-pentane,isopentane, hexane, heptane, Freons® etc.

The rubber-modified styrenic resin composition of the present inventionfinds its applications in an injection molded article field, an extrudedsheet field and a foam article filed, in which the properties of thecomposition are best used. That is, as the injection molded article orextrusion molded article, there are exemplified housings of electronicequipments, business appliances, telephones, office automationequipments, etc. and wrapping materials such as food containers. Thefoam material is used in the production of wrapping containers by vacuumshaping or pressure shaping. In addition, the rubber-modified styrenicresin composition of the present invention is preferably used as acushioning material for precision machines, a heat insulator, aconstruction material, and so on.

EXAMPLES

The present invention will be illustrated by the following examples,which do not limit the scope of the present invention in any way.

The measurements and evaluations are carried out as follows. Theproperties other than those described below were measured by the abovedescribed methods.

(1) Flexural modulus (stiffness)

Flexural modulus was measured according to JIS K7203.

(2) Vicat softening point (heat resistance)

A Vicat softening point was measured according to JIS K7206, Method B.

(3) DuPont type impact strength (plane impact strength)

A plate having a thickness of 2 mm was injection molded. Using anapparatus having a dart tip diameter of 1/8 inch R and a receivingdiameter of 3/16 R, an energy at 50% destruction was measured at 23° C.As a molding apparatus, Toshiba IS-150E was used, a mold temperature was40° C., and sample sizes were 150×90×2 mm. With a resin sheet, using anapparatus having a dart tip diameter of 1/8 inch R and a receivingdiameter of 3/16 R, an energy at 50% destruction was measured at 23° C.

(4) Failing weight impact (plane impact strength)

A plate having a thickness of 2 mm was injection molded. Using a"falling weight graphic impact tester" of TOYO SEIKI MANUFACTURING Co.,Ltd., a weight of 7.5 kg was spontaneously fallen from a height of 80 cmon a surface of the plate to completely break or pass through the plateby a striker which was attached to a lower end of the weight. Then, anenergy required for cracking the plate was measured. As a moldingapparatus, Toshiba IS-150E was used, a mold temperature was 40° C., andsample sizes were 150×90×2 mm.

(5) Surface gloss (surface appearance)

A plate having a thickness of 2 mm was injection molded. Gloss in acentral area of the plate was measured by the method for measuring 45degrees mirror surface gloss of JIS K7105. As a molding apparatus,Toshiba IS-150E was used, a mold temperature was 40° C., and samplesizes were 150×90×2 mm. With the resin sheet, the surface gloss wasmeasured in the same manner.

(6) Tensile modulus (stiffness)

Using a resin sheet, tensile modulus was measured according to JISK7113.

Examples 1-10 and Comparative Examples 1-9

Components shown in Tables 1-4 were molten, kneaded and pelletized by anextruder having a cylinder diameter of 40 mm at 220° C. to obtainpellets. The obtained pellets were injection molded to form a test pieceor a plate, and subjected to the above measurements of the physicalproperties.

Examples 11 and 12 and Comparative Example 10

Components in Table 5 were dry blended and extrusion molded using asheet processing machine having a cylinder diameter of 65 mm (V65-S1000manufactured by TANABE PLASTICS MACHINE) at a resin temperature of 240°C. to obtain a resin sheet having a thickness of 1.2 to 1.5 mm. Physicalproperties of the sheet were measured.

The used rubber-modified styrenic resin (A) was synthesized by acontinuous bulk polymerization method as follows:

Component (A) used in Examples 1-12 and Comparative Examples 1-6 and 10

In a polymerization vessel equipped with a stirrer, a liquid mixture of80 wt. % of styrene, 12 wt % of a styrene-butadiene block copolymer(styrene content of 40 wt. %), 5 wt. % of ethylbenzene and 3 wt. % of amineral oil was supplied and polymerized at a temperature of 140° C. ata stirring rate of 35 rpm to a conversion of 37.5%. Subsequently, theresulting liquid mixture was transferred to a liquid filling typepolymerization vessel and polymerized to a conversion of 77%. A contentwas transferred to an evacuation vessel kept at 240° C. and volatilecomponents were evaporated off. Then, the obtained polymer was passedthrough a melt extruder and a pelletizer to obtain a pellet formrubber-modified styrenic resin.

Component (A) used in Comparative Example 7

In a polymerization vessel equipped with a stirrer, a liquid mixture of89.8 wt. % of styrene, 5.6 wt % of polybutadiene, 3.6 wt. % ofethylbenzene and 1 wt. % of a mineral oil was supplied and polymerizedat a temperature of 140° C. at a stirring rate of 60 rpm to a conversionof 23%. Subsequently, the resulting liquid mixture was transferred to aliquid filling type polymerization vessel and polymerized to aconversion of 70%. A content was transferred to an evacuation vesselkept at 240° C. and volatile components were evaporated off. Then, theobtained polymer was passed through a melt extruder and a pelletizer toobtain a pellet form rubber-modified styrenic resin.

Component (A) used in Comparative Examples 8 and 9

In a polymerization vessel equipped with a stirrer, a liquid mixture of87.4 wt. % of styrene, 5.4 wt % of polybutadiene, 5 wt. % ofethylbenzene and 2.2 wt. % of a mineral oil was supplied and polymerizedat a temperature of 140° C. at a stirring rate of 35 rpm to a conversionof 20%. Subsequently, the resulting liquid mixture was transferred to aliquid filling type polymerization vessel and polymerized to aconversion of 70%. A content was transferred to an evacuation vesselkept at 240° C. and volatile components were evaporated off. Then, theobtained polymer was passed through a melt extruder and a pelletizer toobtain a pellet form rubber-modified styrenic resin.

The used polymers (B) were as follows:

B1: Ethylene-methyl methacrylate copolymer (Trade name "ACRYFT WM 403"manufactured by Sumitomo Chemical Co., Ltd. Methyl methacrylate content:38 wt. %. Melt flow rate: 15 g/10 min.)

B2: Ethylene-methyl methacrylate copolymer (Trade name "ACRYFT WK 402"manufactured by Sumitomo Chemical Co., Ltd. Methyl methacrylate content:25 wt. %. Melt flow rate: 20 g/10 min.)

B3: Ethylene-methyl methacrylate copolymer (Trade name "ACRYFT WH 303"manufactured by Sumitomo Chemical Co., Ltd. Methyl methacrylate content:18 wt. %. Melt flow rate: 7 g/10 min.)

B4: Ethylene-ethyl acrylate copolymer (Ethyl acrylate content: 18 wt. %.Melt flow rate: 7 g/10 min.)

B5: Ethylene-vinyl acetate copolymer (Trade name "SUMITATE RG-11"manufactured by Sumitomo Chemical Co., Ltd. Vinyl acetate content: 41wt. %. Melt flow rate: 60 g/10 min.)

B6: Ethylene-vinyl acetate copolymer (Trade name "SUMITATE HA-20"manufactured by Sumitomo Chemical Co., Ltd. Vinyl acetate content: 20wt. %. Melt flow rate: 20 g/10 min.)

B7: Polypropylene (Trade name "NOBLEN AD571" manufactured by SumitomoChemical Co., Ltd. Melt flow rate: 0.2 g/10 min.)

B8: Polyethylene (Trade name "SUMIKASENα FZ 103-0" manufactured bySumitomo Chemical Co., Ltd. Melt flow rate: 0.9 g/10 min.)

B9: Polymethyl methacrylate (Trade name "SUMIPEKS-BMHG" manufactured bySumitomo Chemical Co., Ltd. Melt flow rate: 0.5 g/10 min.)

B10: Styrene-methyl methacrylate copolymer (Trade name "ESTYRENE MS300"manufactured by SHIN-NITTETSU CHEMICAL INDUSTRIES, LTD. Methylmethacrylate content: 30 wt. %. Melt flow rate: 0.2 g/10 min.)

B11: Styrene-acrylonitrile copolymer (Trade name "SANREX SAN-R"manufactured by MITSUBISHI MONSANTO CHEMICAL Co., Ltd. Acrylonitrilecontent: 26 wt. %. Melt flow rate: 0.9 g/10 min.)

A melt flow rate was measured according to JIS K7210 at a temperature of190° C. under a load of 2.16 kgf. Solubility parameters of thesepolymers (B) are shown in Tables 6 and 7.

As an organic polysiloxane, a silicone oil of TORAY SILICONE, a tradename "SH200" (polydimethylsiloxane, 1000 cSt) was used.

The results indicate the following:

The compositions of Examples satisfying all the conditions of thepresent invention achieved the excellent results in all the evaluations.The composition of Comparative Example 1 containing no polymer (B) hadthe very low plane impact strength (the falling weight impact and DuPonttype impact strength), and slightly poor gloss. The compositions ofComparative Examples 2 to 4 containing the polymer having the SP outsidethe defined range as the polymer (B) were poor in plane impact strength.The compositions of Comparative Examples 5 and 6 containing the polymer(B) which comprised the aromatic vinyl compound units and had the SPoutside the defined range was poor in plane impact strength. Thecompositions of Comparative Examples 7 to 9 which had the large particlesize and the salami structure were poor in plane impact strength andgloss. The molded sheet of Comparative Example 10 containing no polymer(B) was poor in plane impact strength and gloss.

                                      TABLE 1                                     __________________________________________________________________________                 C. Ex. 1                                                                          Ex. 1                                                                              Ex. 2                                                                             Ex. 3                                                                             Ex. 4                                                                              Ex. 5                                      __________________________________________________________________________    Composition                                                                     (wt. parts)                                                                   (A)*1) 100 100 100 100 100 100                                                (B)*2) 0 1 1 2 4 6                                                              B1 B1 B1 B1 B1                                                              (C)*3) 0 0 0.05 0.05 0.05 0.1                                                 Structure                                                                     Amount of soft component 27 27 27 27 27 27                                    particles in (A)                                                              (wt. %)                                                                       Particle size of soft 0.18 0.18 0.18 0.18 0.18 0.18                           component particles in (A)                                                    (μm)                                                                       Structure of soft component OCC OCC OCC OCC OCC OCC                           particles in (A)*4)                                                           Evaluations                                                                   Flexural moduus 20200 19300 19200 18900 18500 17800                           (kgf/cm.sup.2)                                                                DuPont type impact strength 8.5 15.6 22.6 41.5 46.5 45.0                      (kgf · cm)                                                           Falling weight impact crack 3.0 6.7 8.2 16.5 18.8 18.1                        forming energy (J)                                                            Vicat softening point (° C.) 87.2 86.8 86.8 86.8 85.5 84.0                                               Gloss (%) 103 104 104 104 105             __________________________________________________________________________                                       103                                    

                  TABLE 2                                                         ______________________________________                                                   Ex. 6 Ex. 7   Ex. 8   Ex. 9 Ex. 10                                 ______________________________________                                        Composition                                                                     (wt. parts)                                                                   (A)*1) 100 100 100 100 100                                                    (B)*2) 4 2 2 4 4                                                               B2 B3 B4 B5 B6                                                               (C)*3) 0.1 0.05 0.1 0.1 0.1                                                   Structure                                                                     Amount of soft compo- 27 27 27 27 27                                          nent particles in (A)                                                         (wt. %)                                                                       Particle size of soft 0.18 0.18 0.18 0.18 0.18                                component particles in                                                        (A) (μm)                                                                   Structure of OCC OCC OCC OCC OCC                                              soft component                                                                particles in (A)*4)                                                           Evaluations                                                                   Flexural modulus 18900 18800 19000 17800 18100                                (kgf/cm.sup.2)                                                                DuPont type impact 40.0 38.2 28.3 40.8 46.3                                   strength (kgf · cm)                                                  Falling weight impact 14.5 15.7 10.7 16.8 18.1                                crack forming energy (J)                                                      Vicat softening point 85.5 86.6 86.5 85.1 86.5                                (° C.)                                                                 Gloss (%) 106 105 105 104 103                                               ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                                   C. Ex. 2                                                                            C. Ex. 3                                                                              C. Ex. 4                                                                              C. Ex. 5                                                                            C. Ex. 6                               ______________________________________                                        Composition                                                                     (wt. parts)                                                                   (A)*1) 100 100 100 100 100                                                    (B)*2) 4 4 4 4 4                                                               B7 B8 B9 B10 B11                                                             (C)*3) 0.1 0.1 0.1 0.1 0.1                                                    Structure                                                                     Amount of soft compo- 27 27 27 27 27                                          nent particles in (A)                                                         (wt. %)                                                                       Particle size of soft 0.18 Q18 0.18 0.18 0.18                                 component particles in                                                        (A) (μm)                                                                   Structure of OCC OCC OCC OCC OCC                                              soft component                                                                particles in (A)*4)                                                           Evaluations                                                                   Flexural modulus 20000 19500 20700 20500 20700                                (kgf/cm.sup.2)                                                                DuPont type impact 4.2 7.9 4.4 6.2 5.2                                        strength (kgf · cm)                                                  Falling weight impact 1.1 4.1 1.1 3.7 2.4                                     crack forming energy (J)                                                      Vicat softening point 87.7 86.8 88.1 87.5 87.6                                (° C.)                                                                 Gloss (%) 104 106 105 102 101                                               ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                                        C. Ex. 7                                                                             C. Ex. 8 C. Ex. 9                                      ______________________________________                                        Composition                                                                     (wt. parts)                                                                   (A)*1) 100 100 100                                                            (B)*2) 1 0 4                                                                   B1  B1                                                                       (C)*3) 0.05 0 0.1                                                             Structure                                                                     Amount of soft component 15 14 14                                             particles in (A)                                                              (wt. %)                                                                       Particle size of soft 0.8 1.8 1.8                                             component particles in (A)                                                    (μm)                                                                       Structure of soft component SAL SAL SAL                                       particles in (A)*4)                                                           Evaluations                                                                   Flexural modulus 24500 20900 19900                                            (kgf/cm.sup.2)                                                                DuPont type impact strength 0.5 11.0 13.5                                     (kgf · cm)                                                           Falling weight impact crack 3.7 5.2 5.6                                       forming energy (J)                                                            Vicat softening point (° C.) 80.8 90.0 89.8                            Gloss (%) 101 61 65                                                         ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                                        C. Ex. 10                                                                            Ex. 11   Ex. 12                                        ______________________________________                                        Composition                                                                     (wt. parts)                                                                   (A)*1) 100 100 100                                                            (B)*2) 0 2 4                                                                    B1 B1                                                                       (C)*3) 0 0.05 0.05                                                            Structure                                                                     Amount of soft component 27 27 27                                             particles in (A)                                                              (wt. %)                                                                       Partice size of soft 0.18 0.18 0.18                                           component particles in (A)                                                    (μm)                                                                       Structure of soft component OCC OCC OCC                                       particles in (A)*4)                                                           Evaluations                                                                   DuPont type impact strength 19.4 23.5 32.7                                    (kgf · cm)                                                           Tensile modulus (kgf/cm.sup.2) 10000 9400 9200                                Gloss (%) 102 106 105                                                       ______________________________________                                         Common Notes for Tables 1 to 5:                                               *1) (A): Rubbermodified styrenic resin (styrene being used as a styrenic      monomer).                                                                     *2) (B): Polymers shown in Tables 6 and 7.                                    *3) (C): An organic polysiloxane.                                             *4) OCC: single occlusion; SAL: salamilike.                              

                  TABLE 6                                                         ______________________________________                                               B1    B2      B3      B4    B5    B6                                   ______________________________________                                        Density ρ                                                                          0.96    0.94    0.94  0.93  0.97  0.94                                 (g/cm.sup.3)                                                                  Molecular 38.5 34.1 32.2 32.2 38.7 32.4                                       weight M of                                                                   repeating unit                                                                ΣF.sub.i 341 310 296 298 343 298                                        SP 8.50 8.55 8.64 8.61 8.60 8.65                                            ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                               B7     B8       B9      B10    B11                                     ______________________________________                                        Density ρ                                                                          0.90     0.92     1.19  1.09   1.10                                    (g/cm.sup.3)                                                                  Molecular 42.0 28.0 100 102.8 83.9                                            weight M of                                                                   repeating unit                                                                ΣF.sub.i 375 266 778 860 768                                            SP 8.04 8.74 9.26 9.12 10.07                                                ______________________________________                                    

What is claimed is:
 1. A molded foam article comprising:arubber-modified styrenic resin composition comprising:(A) 100 wt. partsof a rubber-modified styrenic resin which contains 10 to 35 wt. % ofsoft component particles having an average particle size of 0.1 to 0.5μm, wherein said soft component particles have a single occlusionstructure comprising a core part which consists of a single continuousphase of a styrenic resin and a shell part which comprises a rubberpolymer and occludes said core part; and (B) 0.1 to 10 wt. parts of apolymer having a solubility parameter (SP) of 8.45 to 8.70 and having noaromatic vinyl compound unit therein.
 2. The molded foam articleaccording to claim 1, wherein said polymer (B) is a copolymer comprisingethylene and at least one vinyl monomer selected from the groupconsisting of unsaturated carboxylic acids, unsaturated carboxylates andvinyl acetate.
 3. The molded foam article according to claim 1, whereinsaid polymer (B) is an ethylene-unsaturated carboxylate copolymer. 4.The molded foam article according to claim 1, wherein said polymer (B)is an ethylene-methyl methacrylate copolymer.
 5. The molded foam articleaccording to claim 1, wherein said polymer (B) is an ethylene-vinylacetate copolymer.
 6. The molded foam article according to claim 1,which further comprises 0.01 to 0.5 wt. parts of an organic polysiloxaneper 100 wt. parts of said rubber-modified styrenic resin (A).
 7. Themolded foam article according to claim 6, wherein the organicpolysiloxane is a compound of the following formula: ##STR2## wherein R₁and R₂ are the same or different and represent an alkyl group, an arylgroup or a phenyl group; and n represents an average degree ofpolymerization and is a number of 10 to
 1500. 8. The molded foam articleaccording to claim 1, wherein said styrenic resin is obtained bypolymerizing at least one styrenic monomer selected from styrene,alpha-methylstyrene and p-methylstyrene.
 9. The molded foam articleaccording to claim 1, wherein said styrenic resin is obtained bypolymerizing at least one styrenic monomer selected from the groupconsisting of styrene, alpha-methylstyrene and p-methylstyrene; and acopolymerizable compound selected from the group consisting ofacrylonitrile, methacrylonitrile, methacrylic acid, methyl methacrylate,maleic anhydride, and maleimide.
 10. The molded foam article accordingto claim 1, wherein said rubber polymer is selected from the groupconsisting of polybutadiene, styrene-butadiene copolymer, andethylene-propylene-non-conjugated diene terpolymer.
 11. The molded foamarticle according to claim 1, wherein the soft component particles havean average particle size of 0.1 to 0.3 μm.